Apparauts for rod displacement crucible-free zone melting

ABSTRACT

Apparatus for crucible-free zone melting a crystalline rod comprising a melting zone chamber having a substantially horizontal wall formed with an opening therein, a slide member adjacent the horizontal wall outside of the chamber for sealingly covering the opening, a pair of spaced holders mounted in the chamber for vertically end supporting a crystalline rod between them, means for relatively displacing the end holders toward one another, an annular heating device surrounding and spaced from the rod and adapted to form a molten zone in the rod wherefrom a portion of the rod recrystallizes, means for displacing the slide member and the rod holder for the recrystallizing rod portion in a substantially horizontal direction transverse to the axis of the rod, and means for rotating at least the rod holder for the recrystallizing rod portion comprising a drive shaft extending vacuum-tightly through an opening in the slide member and the opening in the wall and connected to the rotatable holder in the chamber.

United States Patent Appl. No. Filed Patented Assignee Priority APPARATUS FOR ROD DISPLACEMENT CRUClBLE-FREE ZONE MELTllNG 6 Claims, 3 Drawing Figs.

[1.8. cu 23/273 SP, 23/301 SP 1m. (:1 B01j 17/10 FieldofSearch 23/3o1sP, 273 SP References Cited UNITED STATES PATENTS 7/1968 Emeis 4/1962 Emeis. 1/1966 Larsen 23/273 SP 23/301 23/301 X 3,359,077 12/1967 Arst 23/273 3,370,927 2/1968 Faust... 23/273 3,414,388 12/1968 Keller 23/273x Primary Examiner-Norman Yudkoff Assistant Examiner-R. T. Foster Attorneys-Curt M. Avery, Arthur E. Wilfond, Herbert L.

Lerner and Daniel J. Tick ABSTRACT: Apparatus for crucible-free zone melting a crystalline rod comprising a melting zone chamber having a substantially horizontal wall formed with an opening therein, a slide member adjacent the horizontal wall outside of the chamber for sealingly covering the opening, a pair of spaced holders mounted in the chamber for vertically end supporting a crystalline rod between them, means for relatively displacing the end holders toward one another, an annular heating device surrounding and spaced from the rod and adapted to form a molten zone in the rod wherefrom .a portion of the rod recrystallizes, means for displacing the slide member and the rod holder for the recrystallizing rod portion in a substantially horizontal direction transverse to the axis of the rod, and means for rotating at least the rod holder for the recrystallizing rod portion comprising a drive shaft extending vacuumtightly through an opening in the slide member and the opening in the wall and connected to the rotatable holder in the chamber.

PATENTEDBCT 2 6 IQH SHEET NF 2 APPARATUS FOR ROD DISPLACEMENT CRUCIBLE- FREE ZONE MELTING Our invention relates to apparatus for crucible-free zone melting a crystalline rod, especially a semiconductor rod.

In the copending application Ser. No. 428,933 of W. Keller filed Jan. 29, I965 and assigned to the assignee of the instant application, there is described a method of crucible-free zone melting a crystalline rod, especially a semiconductor rod vertically end supported by a pair of end holders, at least one of which is rotated about its vertical axis and is displaceable in the direction of its rotary axis relative to an annular heating device surrounding the rod, the rotating holder being also laterally displaceable relative to the heating device. The rod portion resolidifying from the melting zone can be located selectively beneath or above the heating device.

The method of the aforementioned copending application permits the production of semiconductor rods, preferably silicon rods, having greater cross sections than the prior concentric or coaxial type of zone melting. It has been found that the aforedescribed method can be applied with great advantage to semiconductor rods that are not compressed in the axial direction thereof, i.e. for methods wherein the resolidifying rod portion has the same or smaller cross-sectional dimensions than those of the rod portion supplied to the melting zone. The crystal quality is thereby particularly improved and the radial resistance distribution over the cross section of the rod is equalized.

It is accordingly an object of our invention to provide improved apparatus for carrying out the method of the aforementioned copending application.

With the foregoing and other objects in view, we provide, in accordance with the invention, apparatus wherein at least the drive shaft for the holder of the resolidifying rod portion extends vacuumtightly through a laterally displaceable slide member located on a substantially horizontal wall of zone melting chamber, and the slide member, in turn vacuumtightly closes an opening in the wall provided for permitting lateral displacement of the drive shaft.

In accordance with other features of our invention, the slide member can not only be displaced in one direction, but also the lateral displacement advantageously takes place repeatedly during the performance of the method in directions opposite to one another, for example, about times per minute. Instead of a linear reciprocatory motion, the slide member can also execute a circular motion, preferably eccentric to the axis of the other rod holder which is not laterally displaceable. This type of motion is marked by the fact that it is shock free.

In accordance with further features of our invention, there is provided in at least one of the two contacting surfaces between the substantially horizontal zone melting chamber wall and the slide member, a groove completely surrounding the opening formed in the substantially horizontal zone melting chamber wall, which is filled with a sealing liquid, preferably oil, and for every position of the slide member, the groove remains covered by the slide member. Such a construction is particularly easy moving because a liquid film is applied over the largest part of the two contacting surfaces of the slide member and the substantially horizontal wall of the zone melting chamber, whereby friction between the contacting surfaces is diminished. On the other hand there are no abrading elements located between the two contacting surfaces.

Other features which are considered as characteristic for the invention are set forth in the appended claims.

Although the invention is illustrated and described herein as apparatus for crucible-free zone melting a crystalline rod, especially a semiconductor rod, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.

The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

FIG. 1 is a longitudinal sectional view of an embodiment of the apparatus of our invention showing a laterally displaceable upper rod holder in starting position wherein it is concentric or coaxial with a nonillustrated lower rod holder;

FIG. 2 is a top plan view of FIG. l; and

FIG. 3 is a sectional view of another embodiment of the apparatus of FIG. I showing in eccentric position an upper rod holder eccentrically displaceable relative to the axis of the lower rod holder.

Referring now to the drawings and first particularly to FIG. ll thereof, there is shown a partial cross-sectional view of the zone melting chamber 1 through an opening 17 in a substantially horizontal wall 2 of the zone melting chamber l and through an opening in a laterally displaceable slide member 6. A drive shaft 3 for a holder 4 extends vacuum-sealed into the chamber 1. A crystalline rod 7 formed of the resolidifying rod portion 5 and a supply rod portion 9 supplying a melting zone 8 located therebetween is substantially vertically mounted between the upper holder 4 and a nonillustrated lower holder. A groove 10 closed on itself is formed in the substantially horizontal wall 2 of the zone melting chamber and is filled with a sealing liquid, preferably oil. The slide member 6 is so disposed that in all positions thereof it covers the groove on all sides thereof and thereby provides a vacuumtight seal between the contacting surfaces Ill and 12 of the slide member 6 and the substantially horizontal melting chamber wall 2. The drive shaft 3 for the resolidifying rod portion 5 is rotatable by known (not illustrated) driving means and can furthermore be displaced in the direction of the rod axis relative to the preferably stationary heating device 13. The vacuumtight passage of the drive shaft 3, through an opening in the slide member 6, is provided by known sealing members, such as labyrinth seal or so-called Simmer rings I4. The sealing rings 14 are held in a socket 15 which is itself sealed by a sealing ring 16. In order to eliminate the lateral displacement of the slide member 6, a stop member 18 surrounding the opening 117 for the drive shaft 3 of the rod holder 4 is mounted advantageously on the substantially horizontal zone melting chamber wall 12. The stop member 118 has a sealing ring 19 which prevents sealing liquid located in the groove l0 and between the mutually adjacent contacting surfaces II and 12 from entering the zone melting chamber 11. On the free face 20 of the slide member 6, spacer holders 21 are mounted whereon a carrier plate 22 is secured. The drive mechanism for the drive shaft of the rod holder 4 can be mounted on the carrier plate 22.

A nut 23 is laterally embedded in the slide member I1 and cooperates with a spindle 24 mounted on the slide member 6. The spindle 24 can either be actuated by hand or by a drive mechanism such as, for example, a. reversing motor (not shown). Guide rails 25, as seen more clearly in the top plan view of FIG. 2, provide good guidance for the slide member 6 as it is being laterally displaced.

It is apparent that details of the illustrated and described embodiment of FIGS. 1 and 2 can be varied without departing from the scope of the invention. Thus, for example, instead of the sealing liquid in the endless groove 10, an elastic sealing element, for example, a sealing ring can be inserted in the groove. As noted hereinabove, instead of a spindle guide on the slide member 6, an eccentric device can be coupled thereto, which urges the slide member 6 to execute a circular motion eccentric to the axis of the nonillustrated lower rod holder.

A device of the just-mentioned type is shown in FIG. 3. The structural features of FIG. 3, which are similar to those of FIG. ll, are identified by correspondingly similar reference numerals. To produce the eccentric motion of the resolidifying rod portion 5 relative to the rod portion 9 supplied to the melting zone 8, an eccentric 27 is secured to a flat side 26 of the slide member 6, the eccentric 27 being rotated by a worm "um" Mun drive 28. Consequently, a considerably shockproof lateral displacement of the rod portion 5 with respect to the rod portion 9 is obtained with simultaneous relatively good intermixing of the melting zone 8. This is of great importance in obtaining a uniform radial resistance distribution over the rod cross section and relatively good crystal quality of the semiconductor rod 7 under treatment.

The inventive coordination of the slide member 6 and the one substantially horizontal melting chamber wall 2 can also exist at the opposite nonillustrated other substantially horizontal wall of the melting chamber. Therewith the rod portion 9 of the crystalline rod 7 supplying the melting zone 8 can also be laterally displaced. Such a construction is particularly advantageous if the slide member 6 executes the eccentric circular motion shown in H6. 3, because in such a case the stirring effect of both rod portions 5 and 9 on the melting zone is increased, which causes an especially unifonn radial resistance distribution. This last-mentioned construction is advantageously selected if the heating device is mounted above the resolidifying or recrystallizing rod portion 5. The axial speed of both rod portions 5 and 9 can either be the same or different. The aforedescribed devices can be used both for pulling monocrystalline rods which are thinner or which are thicker than the polycrystalline supply rods.

We claim:

1. Apparatus for crucible-free zone melting a crystalline rod comprising a melting zone chamber having a substantially horizontal wall formed with an opening therein, a slide member adjacent said substantially horizontal wall outside of said chamber for sealingly covering said opening, a pair of spaced holders mounted in said chamber for vertically end supporting a crystalline rod between them, means for relatively displacing said end holders toward one another, an annular heating device surrounding and spaced from the rod and adapted to form a molten zone in the rod wherefrom a portion of the rod recrystallizes, means for displacing said slide member and the rod holder for the recrystallizing rod portion in a substantially horizontal direction transverse to the axis of the rod, and means for rotating at least the rod holder for the recrystallizing rod portion comprising a drive shaft extending vacuumtightly through an opening in said slide member and said opening in said wall and connected to said rotatable holder in said chamber.

2. Apparatus according to claim 1, wherein said substantially horizontal wall and said slide member have mutually contacting surfaces, at least one of said surfaces being formed with a continuous groove completely surrounding said opening in said substantially horizontal wall, said groove being filled with sealing fluid and being covered by said displaceable slide member in every portion thereof.

3. Apparatus according to claim 1, wherein said substantially horizontal wall and said slide member have mutually contacting surfaces, at least one of said surfaces being formed with a continuous groove completely surrounding said opening in said substantially horizontal wall, and an elastic sealing member received in said groove.

4. Apparatus according to claim 3, wherein said sealing member is a sealing ring.

5. Apparatus according to claim 1, further comprising a liquid-sealed stop member for said slide member located on said substantially horizontal chamber wall and completely surrounding said opening in said wall.

6. Apparatus according to claim 1, wherein said lateral displacing means for said slide member comprises a spindle mounted on said substantially horizontal chamber wall. 

2. Apparatus according to claim 1, wherein said substantially horizontal wall and said slide member have mutually contacting surfaces, at least one of said surfaces being formed with a continuous groove completely surrounding said opening in said substantially horizontal wall, said groove being filled with sealing fluid and being covered by said displaceable slide member in every portion thereof.
 3. Apparatus according to claim 1, wherein said substantially horizontal wall and said slide member have mutually contacting surfaces, at least one of said surfaces being formed with a continuous groove completely surrounding said opening in said substantially horizontal wall, and an elastic sealing member received in said groove.
 4. Apparatus according to claim 3, wherein said sealing member is a sealing ring.
 5. Apparatus according to claim 1, further comprising a liquid-sealed stop member for said slide member located on said substantially horizontal chamber wall and completely surrounding said opening in said wall.
 6. Apparatus according to claim 1, wherein said lateral displacing means for said slide member comprises a spindle mounted on said substantially horizontal chamber wall. 